1. Field of the Invention
The invention relates in general to a circuit and method for generating reference voltage and reference current, and more particularly to a circuit and method for generating temperature-independent reference voltage and reference current.
2. Description of the Related Art
Temperature-independent reference voltage and/or temperature-independent reference current are often applied in design of integrated circuits, which are normally generated by band-gap reference circuits.
For example, in order to generate a temperature-independent reference voltage (i.e. having a zero temperature coefficient), a bipolar transistor featuring a negative temperature coefficient is usually used to generate a voltage with a negative temperature coefficient, and a resistor featuring a conversion ability is used to convert a current with a positive temperature coefficient into a voltage with a positive temperature coefficient. Finally, the negative-temperature-coefficient voltage and the positive-temperature-coefficient voltage are summed by weight to obtain the zero-temperature-coefficient reference voltage. On the other hand, in order to generate a temperature-independent reference current, a bipolar transistor featuring a negative temperature coefficient and a resistor featuring a conversion ability are used to generate a negative-temperature-coefficient current. And finally, the negative-temperature-coefficient current is summed by weight with a positive-temperature-coefficient current to obtain a zero-temperature-coefficient current.
In practical applications, it is common to use at the same time both the temperature-independent reference voltage and the temperature-independent reference current. In such cases, for example, it can be designed to generate the temperature-independent reference voltage by using a band-gap reference circuit and generate the temperature-independent reference current by using another band-gap reference circuit. Alternatively, it can be designed to first generate a reference current (or reference voltage) with a zero temperature coefficient, and then use an extra circuit to mirror and convert the zero-temperature-coefficient reference current (or reference voltage) into a zero-temperature-coefficient reference voltage (or reference current). The extra circuit normally has a bias current source for duplicating a current (or a voltage) and at least a resistor for converting a current into a voltage (or converting a voltage into a current).
However, the conventional circuit usually requires a large number of devices, thus occupying a large chip area and taking large power consumption and production costs. One of the reasons is that, in conception of circuit design, the generation of reference voltage and the generation of reference current are not integrated. Consequently, it has become one of industrial endeavors in search and development to design a simple circuit which can simultaneously generate zero-temperature-coefficient reference voltage and reference current.